Many experts foresee increasing usage of methanol (methyl alcohol) as a fuel in spark-ignited automotive engines. Methanol can be produced from such materials as natural gas, coal or other abundant natural products. Therefore, it offers considerable promise as a replacement for gasoline to power automotive vehicles. A difficulty with the use of methanol in such application is its low volatility. At ambient temperatures of 10.degree. C. and lower, it is difficult to provide methanol vapors in sufficient quantities to start the engine. The vapor pressure of the methanol is too low and the methanol vapor condenses on cold engine surfaces.
One approach to the cold starting of methanol-fueled engines is to employ a second, more volatile fuel such as gasoline or propane. The engine can readily be started through the use of such a second fuel, but the storage and controlled delivery of the second fuel adds complexity to the system.
It has been recognized that methanol can be dissociated into carbon monoxide and hydrogen, two noncondensable gases that can be readily used as produced on board the vehicle to start the engine. The engine would be operated using carbon monoxide and hydrogen as at least part of the fuel charge until it is warm enough to be operated solely on liquid methanol. There are no catalysts which will dissociate methanol at temperatures near room temperature or below at the rates required to start an engine. Thus, if a catalyst is to be employed to dissociate methanol, supplemental heat must be used in a cold starting system to raise the catalyst temperature to approximately 250.degree. C. to 300.degree. C. where rapid methanol dissociation occurs. Moreover, heat must be continually supplied to the catalyst to overcome heat losses associated with both methanol vaporization and the endothermic dissociation reaction.
Yoon, U.S. Pat. No. 4,488,517, discloses a cold start method for methanol-fueled cars. A quantity of liquid methanol is vaporized employing electrical resistance heating. A catalytic dissociation reactor is heated by electrical resistance to a desired temperature. The methanol vapor is mixed with air and the mixture conveyed to the dissociation reactor where partial combustion of the vaporized alcohol occurs as well as dissociation of some of the alcohol to form a mixture that contains hydrogen and carbon monoxide. The hydrogen-carbon monoxide containing mixture is employed in the starting of the engine. A difficulty with the Yoon system is that it requires vaporization and superheating of methanol and storage of the vapor. Such a system is both bulky and complicated in its valving and flow configuration. It is also wasteful of electrical energy.
It is an object of our invention to provide a compact system for cold starting a methanol-fueled engine that utilizes an ultrasonic nozzle to introduce and dispense microdrops of methanol into an air stream to form suitable air-methanol mixtures for both heating a dissociation catalyst by oxidation of the methanol and for dissociating a portion of the methanol to provide carbon monoxide and hydrogen as a fuel constituent to start the engine.
Another object of our invention is to provide a method of generating and employing mixtures of microdroplets of methanol and air of varying composition to provide requisite heat for a dissociation catalyst such that suitable quantities of carbon monoxide and hydrogen are efficiently formed for starting of the vehicle engine.